using UnityEngine;

//-----------------------------------------------------------------------------
// Copyright 2014-2020 RenderHeads Ltd.  All rights reserved.
//-----------------------------------------------------------------------------

namespace RenderHeads.Media.AVProDeckLink
{
	public class PrefabSingleton<T> : MonoBehaviour where T : MonoBehaviour
	{
		private static T _instance;

		private static object _lock = new object();

		public static T Instance
		{
			get
			{
				if (applicationIsQuitting)
				{
					return null;
				}

				lock (_lock)
				{
					if (_instance == null)
					{
						_instance = (T)FindObjectOfType(typeof(T));

						if (FindObjectsOfType(typeof(T)).Length > 1)
						{
							Debug.LogError("[Prefab Singleton] Something went really wrong " +
								" - there should never be more than 1 singleton!" +
								" Reopenning the scene might fix it.");
							return _instance;
						}

						if (_instance == null)
						{
							T[] singleton = (T[])Resources.FindObjectsOfTypeAll(typeof(T));

							if(singleton.Length > 1)
							{
								Debug.LogError("[Prefab Singleton] There should be only one instance of a prefab singleton " + singleton.Length + " found instead");
								return null;
							}
							else if(singleton.Length == 0)
							{
								Resources.Load("DeviceExplorerManager(Singleton)");

								singleton = (T[])Resources.FindObjectsOfTypeAll(typeof(T));

								if (singleton.Length != 1)
								{
									Debug.LogError("[Prefab Singleton] There should be only one instance of a prefab singleton " + singleton.Length + " found instead");
									return null;
								}
							}

							_instance = (T)Instantiate(singleton[0]);

							DontDestroyOnLoad(_instance);
						}
					}

					return _instance;
				}
			}
		}

		private static bool applicationIsQuitting = false;

		public void OnDestroy()
		{
			applicationIsQuitting = true;
		}
	}
}